110.34 1&2

[Ranch]

Situation: 15kV switchgear, with six feet clearance from a metal wall meeting 110.34 condition 2.

Now assume there is a a need to push the gear forward 6inches. Could the wall be insulated (lined with insulative fiber type board), meet 110.34 condition 1, in order not to have to move the wall?

 

[charlie b]

Yes you could do that. I have done similar things, when clearance was tight. But in this case, you don't have to! :smile: You only need 5 feet of working clearance. You have 15kV gear, but that is a phase to phase value. The voltage to ground is 8,660. That puts you in the second row of Table 110.34(A), not the third.

 

[Ranch]

Exactly - thank you Charles. I looked right past that 9000V mark.

 

[Ranch]

OK ? one more on 110.34

4,160V system, P-N = ~ 2400V

Customer taps up supply 5%, ~ 4,370V, we slide up over 2,500V P-N and perhaps we could make the case you slide down a row on 110.34

Am I making sense? I ponder all the time if it is our calculators, equipment nameplates and drawings or our meters that should govern the numbers in our interpretations. I wonder about the science behind how the 110.26 and 110.34 ranges are determined.

 

[charlie b]

Take another look at the table. It speaks of "nominal voltage to ground," not of "actual measured voltage to ground." In a 4160 volt system, that value is 2400 volts, no matter what you do with the taps.